Hyungjoon Seo
Deparment: Department of Civil Engineering

Items: 9

Views: 10371

1. Distributed Fiber Optic Sensing of Axially Loaded Bored Piles

Author:Pelecanos, L;Soga, K;Elshafie, MZEB;de Battista, N;Kechavarzi, C;Gue, CY;Ouyang, Y;Seo, HJ


Abstract:Instrumented pile tests are vital to establish the performance of a pile and validate the assumptions made during initial design. Conventional instrumentation includes vibrating wire strain gauges and extensometers to measure the change in strain or displacements within a pile. Although these strain and displacement gauges are very accurate, they only provide strain/displacement readings at discrete locations at which they are installed. It is therefore common to interpolate between two consecutive points to obtain values corresponding to the data gaps between points; in practice, these discrete instrumented points could be tens of meters apart, at depths corresponding to different soil layers, and hence simple interpolation between the measurement points remains questionable. The Brillouin optical time-domain reflectometry fiber optic strain sensing system is able to provide distributed strain sensing along the entire length of the cable, enabling the full strain profile to be measured during a maintained pile load test. The strain data can also be integrated to obtain the displacement profile. This paper presents three case studies which investigate the performance of three concrete bored piles in London using both conventional vibrating wire strain gauges and distributed fiber optic strain sensing during maintained pile load tests, which enable comparisons made between the two instrumentation systems. In addition, finite-element analyses show that the ability to measure the full strain profiles for each pile is highly advantageous in understanding the performance of the pile and in detecting any abnormalities in the pile behavior. (C) 2017 American Society of Civil Engineers.
2. Crack Detection in Pillars Using Infrared Thermographic Imaging

Author:Seo, H;Choi, H;Park, J;Park, J;Lee, IM


Abstract:In this paper, we describe a series of crack-detection tests on scale models of cavern supported by pillars performed in the laboratory to find out where and when crack initiation occurs. Crack initiation was detected by two different methods, thermographic camera imaging and strain-gauge measurements, and comparisons were drawn. For the crack-detection test, three physical models of pillars were made out of gypsum with different pillar widths (25 mm, 50 mm, and 100 mm). When cracks begin to develop in the pillar models, a thermographic camera can detect temperature changes around the cracks that are induced by friction at the contact areas. Whereas the strain-gauge measurement indicates only local strains, the thermographic imaging can cover overall strain variations. The authors did not correlate the increase in temperature variations with strain. With the 50-mm and 100-mm pillar widths in the laboratory test, the crack-induced failure naturally occurred in three steps: (1) first crack initiation, (2) crack propagation, and (3) failure. But for the 25-mm pillar width, the crack-induced failure occurred immediately after the first crack initiation; propagation was not observed.
3. Crack detection in frozen soils using infrared camera

Author:Zhao, Yang ; Li, Rui ; Seo, Hyungjoon

Source:ISARC 2018 - 35th International Symposium on Automation and Robotics in Construction and International AEC/FM Hackathon The Future of Building Things,2018,Vol.

Abstract:Frozen soils are encountered on construction site in the polar regions or where artificial frozen ground (AFG) method is used. Thus, efficient ways to monitor the behaviour and potential failure of frozen soils are on demand. The advance in thermographic technology presented an alternative solution as the deformation occurred in frozen soil would generate inter-particle friction heat, and hence increase in temperature. In this research, uniaxial compression tests were conducted on cylindrical frozen soil specimens of three types, namely clay, sand and gravel. During the tests, the surface temperature profiles of the specimens were recorded by an infrared video camera. The thermographic videos were analysed, and the results shows that temperature increase caused by frictional heat can be observed in all three frozen soil specimens. Therefore, such temperature increase can be deemed as an indicator for the potential failure of frozen soil and such method is applicable for monitoring purpose. © ISARC 2018 - 35th International Symposium on Automation and Robotics in Construction and International AEC/FM Hackathon The Future of Building Things. All rights reserved.
4. Finite element analysis of soil-structure interaction in soil anchor pull-out tests

Author:Seo, HJ;Pelecanos, L


Abstract:This study presents new data from soil anchor field pull-out tests that were carried out on in-situ ground anchor systems, using strain gauges to evaluate the changes in the variations of axial load and skin friction along the nail during the tests. The results of these field tests provide details about the development of skin friction with induced displacements, thus offering the opportunity to perform load-transfer analyses of the soil anchor. A Finite Element (FE) model based on the load-transfer approach is set up to analyse this problem. The nonlinear load-transfer (t-z) relation requires 3 distinct parameters to be defined, which are related to the initial soil stiffness, stiffness degradation and ultimate strength. These parameters are defined from the field test data. Subsequent FE analyses using these parameters are run to validate the new load-transfer models which are compared with the field test results and exhibit an excellent agreement.
5. Net load-displacement estimation in soil-nail pullout tests

Author:Seo, HJ;Pelecanos, L;Kwon, YS;Lee, IM


Abstract:Soil-nails are used to stabilise a soil mass by exploiting the resistance generated by the skin friction between the ground and grout and the tensile stiffness of the reinforcing material. A load-displacement curve is obtained from in situ pullout load tests performed by considering the elastic shear modulus and ultimate skin friction capacity between the soil and grout. This study determines the shear behaviour between the soils and grout analytically, especially the soil-dilation effect during shearing that is one of the main factors affecting the ultimate skin friction, even though this estimation is rather cumbersome. Many studies assume a full bond between the grout and the steel reinforcing bar, thus neglecting their relative displacement. In this study, the net load-displacement between the ground and grout is obtained by subtracting the nail elongation from the load-displacement of the pullout tests when estimating the shear displacement. Numerous field pullout tests are performed in this study under various ground conditions and through various construction methods. The dilatancy angles are estimated dependent on the soil type by comparing the net load-displacement curve obtained in the field with that obtained theoretically.
6. Role of induced electrical polarization to identify soft ground/fractured rock conditions

Author:Park, J;Lee, KH;Seo, H;Ryu, J;Lee, IM


Abstract:This study attempted to evaluate the role and effectiveness of induced polarization (IP) along with electrical resistivity to identify soft ground/fractured rock. Theoretical studies as well as laboratory-scale experiments were conducted for this purpose. The theoretical study involved deriving the functional relationship between chargeability and influential variables. This was followed by performing a sensitivity analysis using the derived relationship to reveal that the size of narrow pores (r(1)) exerted the greatest influence on the chargeability followed by the salinity of the pore water (C-0). In the laboratory test, a small-scale fractured rock zone was modeled using sandstone as a parent rock. The chargeability and resistivity were measured by changing the size of the joint aperture filled with tap water and/or sea water, the location of the fractured zone, and the thickness of the soil layer in a soil-rock multi-layered ground. The experimental study modeled the jointed zone between competent sandstone layers and indicated that the chargeability was mostly controlled by the size of the narrow pore (r(1)) of the surface sandstone and not by the porosity of the jointed zone. Hence, it was concluded that the chargeability did not significantly depend on the fractured characteristics of the jointed rock. It could be difficult to clearly distinguish as to whether the low resistivity value is caused by the sea water intrusion or by the increase in porosity of the fractured ground. However, the IP exploration can be effectively utilized to identify sea water intrusion since the chargeability decreased. as the salinity of pore water increased. The experimental study on a soil-rock multi-layered ground indicated that the measured chargeability was controlled by the percentage of current flow that passed through the competent rock as well as by the narrow pore size of the rock itself. In conclusion, the ground condition could be easily identified by measuring the IP in conjunction with the electrical resistivity, and this increased the reliability of identifying the existence of sea water, layered ground, and/or the fractured rock. (C) 2016 Elsevier B.V. All rights reserved.
7. Mechanical Behavior of Hybrid Soil Nail-Anchor System

Author:Seo, H;Lee, IM;Ryu, YM;Jung, JH


Abstract:Prestressed soil-nail system has two reinforcing components: steel bar and PC strands. The steel bar with relatively less elongation yields earlier than PC strands. Thus, yield displacements of these two components should be matched to maximize the design load (capacity) of prestressed soil-nail. To achieve this, PC strands need to be prestressed before applying pullout load. In this study, load transfer mechanisms of soil-nail and prestressed soil-nail were determined based on skin friction theory and load transfer theory. The load transfer was derived analytically based on the assumption that skin friction at the interface was fully mobilized. It was then compared with results from field pullout tests performed to identify in-situ load transfer mechanism. Additionally, optimum prestress level required to maximize the pullout loading capacity was evaluated and compared with those obtained from field tests.
8. Monitoring of retaining structures on an open excavation site with 3D laser scanning

Author:Seo,H. J.;Zhao,Y.;Wang,J.

Source:International Conference on Smart Infrastructure and Construction 2019, ICSIC 2019: Driving Data-Informed Decision-Making,2019,Vol.

Abstract:Three-dimensional (3D) laser scanning techniques evolved significantly in terms of accuracy and resolution in recent years and now demonstrate a great potential for structural displacement monitoring. Laser scanners can capture the 3D profile of a structure and can be used for displacement monitoring of all visible surfaces. While the traditional techniques (total station, inclinometer, and theodolite measurements) measure displacements sparsely at several sampled points on the structure. In this work, a 3D laser scanner was used to monitor displacement of a ring beam and a reinforced soil mixing wall (SMW) at an open excavation site. Seven scans of the SMW were taken during the excavation. 3D point clouds of the SMW produced with these scans are placed in one consistent coordinates system and the difference between each pairs of consecutive scans were analysed to determine displacements of the SMW. Several cloud comparison methods were applied including C2C, C2M and M3C2 techniques to identify displacements along the height of the SMW. The displacement obtained were validated against displacement measured by inclinometer and total station. It is concluded that the displacement monitoring with 3D laser scanner are sufficient for monitoring of cumulative displacement but not for increment displacement.
9. Monitoring of CFA pile test using three dimensional laser scanning and distributed fiber optic sensors

Author:Seo, H


Abstract:The results obtained during a pile test are dependent on a number of factors. However, conventional monitoring systems like vibrating wire strain gauges and the extensometers can only measure the variations of strain and displacement at discrete locations at which they are installed in a pile. In order to identify the behavior of Continuous Flight Auger (CFA) pile, the distributed fiber optic monitoring system and three-dimensional laser scanning collected the strain and point clouds data during the pile test with conventional vibrating wire strain gauges, extensometers. Based on the Brillouin Optical Time Domain Reflectometry (BOTDR) fiber optic strain profile, the profiles of axial load, skin friction, displacement can be obtained. The fiber optic monitoring system was compared with conventional systems, and it was found that the ability to measure the full strain profiles is highly advantageous in determining the performance of the pile and in detecting the behavior of CFA pile. The displacement of the pile was measured by the LVDT at the top of the pile and the results were compared with the laser scanning results. In this study, the negative skin friction was detected by BOTDR fiber optic strain profile near the top of the CFA pile. It was not able to define the reason of the negative skin friction from the other monitoring systems but the laser scanning results show that the ground movement due to the pull-out force of the anchor pile affects the negative skin friction. Although laser scanning is not able to measure the real-time data during the pile test, the extensive information can be taken into account by the monitored data from three-dimensional laser scanning.
Total 9 results found
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